Amplifying and detecting system



Oct. 12, 1937. H. F. ELLIOTT AMPLIFYING AND DETECTING SYSTEM Filed April 21, 1932 2 Shets-Sheet l INVENTOR Harold FBI/iota BY HIS ATTORNEY I I Oct. 12, 1937. H. F. ELLIOTT I 2,095,321

AMPLIFYING AND DETECTING SYSTEM Filed April 21, 1932 r 2 Sheets-Sheet 2 TEA- Harold FIZZ/iota BY :15 ATTORNEY 4 the cathode and'the anode.

Patented Oct. 12, 1937 PATENT OFFICE AMPLIFYING ANDDETECTING SYSTEM Harold F. Elliott, Palo Alto, Calif.

Application April 21, 1932, Serial No. 606,612

20 Claims. My invention relates to amplifying and'detecting systems and particularly to systemshaving means for maintaining a substantially constant output over a relatively wide range of input potentials. An object of my'invention is the provision of means whereby the governing action. in such a system may be improved. Another object is to provide means whereby the governing action takes place only when input potentials are applied whose peaks exceed a predetermined level. An-

other object is to provide means whereby a single electron tube of simple construction may serve as a governor and at the same time act asa rectifiefand amplifier. An example of the application of my invention is a radio broadcast receiver having an automatic volume control which functions to limit the output of the receiver when the peaks of the incoming signals exceed a predetermined fixed level. Such an arrangement has the advantage of not attenuating weak signals.

Referringto the drawings: Figs. 1 and 2 show electron tubes suitable for carrying out the invention. Fig. 3 shows circuits in a complete radio broadcast receiverincorporating my invention.

Figs. 4, 5 and 6 show alternative circuit arrangements adapted to carrying out the invention.

Referring to l; the tube consists of the customary glass envelope I, a cathode of the uni-potential type 2 having a terminal 3 which may be mounted inthe base of the tube. The cathode is provided with a suitable heater 4 for the purpose of raising its temperature to the emission point. Connections for the heater are shown at 5-4. Numeral B designates an anode and numeral '7 an external connection to the same. The tube is preferably constructed with .two symmetrically placed grids 8 and 9 between For purposes of clarity one of these grids, as 8, is shown in full lines and the other grid, as 9, is shown in dotted lines. Numerals Ill and H designate connections for the grids, which connections may be brought 45 out to terminals on the base. An auxiliary anode [2 may be placed around an extended portion of the cathode, or otherwiseidisposed, so that electrons may be attracted from the cathode to the auxiliary anode. A connection for the auxiliaryanode is shown at l3.

The tube of Fig.2 is substantially the same as thatv of Fig. l exceptthat it is provided with a screen grid I4 having an external connection 15. As is well knowmscreen grids are useful in giv- 55 s elec n tim d s re s a e-spr s; nd

when desired, in electrostatically shielding elementsbetween which it is desiredto avoid interactions. K

The circuits shown in Fig. 3 represent a complete broadcast receiver of the superheterodyne 5 type embodying one form of the features of my invention. Since the general operation of superheterodyne'receivers is'well understood, only the features which are novel and a part of my invention will be described in detail. 10

The functions of the various electron tubes shown in Fig. 3 are as follows: Tube I6 serves to amplify the incoming signals at the frequency at which they are received. Tube H is a detector which serves to mingle the amplified signals with 15 currents of'heterodyning frequency supplied by [oscillator tube l8. Tube I9 is an intermediate frequency amplifier. Tube 20 is a second detector which serves to convert the amplified intermediate frequency signals to audio-frequency 20 signals. Tube 20 serves also to provide poten- V tials for automatic control of the amplification 1 in tubes 5,11 and i9 as will be hereinafter discussed. Tube 2l is an audio-amplifier, or power output tube, which serves to amplify the audio- 125 frequencysignals from tube 20 and transmit them to the speaker. Tube 22, together with the filter capacitors 23-23-23 and inductors 24 and 25, serves to supply direct current potentials for the operation of the aforementioned tubes and their associated circuits. 7 V

Referring-particularly to the second detector tube 20 and its associated connections, the two grids 8 and 9 are preferably connected to opposite 7 terminals of coil 30. Coil 30 may be the second- .35 ary of an intermediate frequency transformer whose primary is coil 3 I. Coils 30 and 3| are preferably, though not necessarily, tuned to resonance at the intermediatefrequency bysuitable capacitors as shown. Coil 30 is preferably provided with a tap at its electrical center. The loadresistor 32, sometimes called the grid-leak, and the by-pass capacitor 33 may be connected as shown in a circuit leading from the center tap on coil 30 to the cathode'2'. This circuit may include a portion of a potentiometer 34--35-36 so arranged as to place an initial positive bias of the order of a few volts upon the grids 8 and 9, for the purpose of avoiding distortion of weak signals due to grid currents or extraneous potentials induced onthe 5 grids. Potentiometer 34-35--36jmay also serve to maintain the cathode 2 at a potential which is positivewith respect to ground. Capacitors 3'! and 38 serve to icy-pass alternating currents in the grid and cathode circuits.

When a signal is tuned in, grids 8 and 9, together with cathode 2, serve as a full wave rectifier whereby signals are converted into a pulsating direct current in resistor 32, with the pulsations corresponding to the modulations of the signals. The two grids 8 .and 9, together with the cathode 2 and anode 6, then serve to amplify the audio-frequency components of the pulsations in resistor 32.

The amplified audio-frequency signals in the anode circuit of tube 20 may be transmitted to a translating device or to an additional stage of amplification by any suitable form of coupling. In Fig. 3 audio-frequency signals from tube 20 are transmitted to the power output tube 2|, which may be of the pentode type, by resistancecapacitance coupling. However it will be understood that transformer coupling orsimpedance coupling may be used, if preferred. The coupling between tube 20 and tube 2! may include a variable element, such as a potentiometer 4| for controlling the input to tube 2| and consequently the output at the speaker.

The auxiliary anode |2 of the tube 20 may be coupled by any convenient method to any convenient point in the system having signal potentials of suitable value for automatic volume control. As one example, in Fig. 3, the auxiliary anode I2 is coupled to the top of coil 3| by capacitor 42. Another example is shown in Fig. 4, wherein coupling capacitor 42 connects to the top of coil 30. Still another example is shown in Fig. 6, wherein the auxiliary anode circuit comprising anode |2, cathode 2, by-pass capacitors 37 and 59, resistors 36 and 43 and coil 58 is inductively coupled with coils 30 and 3!. The choice of coupling is flexible and is dependent upon the constants of the tubes employed and the conditions of operation to be fulfilled. Also, it may be pointed out that it is not essential that the auxiliaryanode be arranged within the tube exactly as shown in Figs. 1 and 2. Any arrangement whereby electrons may be attracted to the auxiliary anode by applying suitable potentials to the latter may be used. Since the matter of obtaining desired internal constants for electron tubes, as well as of matching external circuits to conform with these constants is now well understood, details of these will not be gone into. Whatever the form of coupling used, it will be evident that whenever the potentials applied to anode l2 cause the latter to become positive with respect to cathode 2, electrons will be attracted to it and it will become negatively charged. This negative charge on auxiliary anode l2 may be used to control automatically the amplification of the preceding tubes I6, I? and l9 by transmitting suitable proportions of the negative charge to the grid circuits of these tubes, thereby increasing their bias. With the circuits shown in Fig. 3, this may be conveniently carried out through the medium of resistors 43, 44, 45, 46 and 47 and capacitors 48, 49, 50 and 5|. Resistor 43 serves as a load resistor in the circuit comprising the-auxiliary anode I2 and cathode 2. Resistors .44, 45, 46 and 41, together with capacitors 48, 49, 50 and 5|, serve as filters toprevent alternating currents flowing in the grid circuits ofthe tubes whose amplification isto be controlled.

It will be evident that with the circuit shown in Fig. 3, the auxiliary anode I 2 and its associated automatic volume control circuits become negatively charged only when the peaks of the alternating current potentials applied to the auxiliary anode exceed the amount by which the oathode 2 is maintained positive with respect to ground. By suitably adjusting the potential drop in resistor 36 it is therefore possible to fix the level at which automatic volume control action starts. Resistor 36 may, if desired, be made adjustable or it may be fixed and so proportioned that the governing action of the automatic volume control functions whenever signals are received which fully load, but do not overload, tubes 20 and 2|. If desired, the lower end of resistor 36 may be connected to a negative point in the power supply system in order to obtain amplified potentials for automatic volume control as described in my copending application Serial No. 605,185 filed April 14, 1932.

Choice of the values for the various resistors and capacitors in Fig. 3 will depend upon the constants of the various tubes and operating conditions. The problems pertaining to the selection of suitable internal tube constants and external circuit values are well understood and need not be gone into here. a In general for commercial tubes now on the market resistors and capacitors of the following order may he used in Fig. 3.

Resistor 32 megohm A Resistor 34 ohms 50,000 Resistor 35 do 1,000 Resistor 36 d0- 2,000 Resistor 39 do 100,000 Resistor 41 megohm Resistor 43 do Resistor 44 do 1 Resistor 45 do /2 Resistor 46 do Resistor 47 do Capacitor 33 micro-microfarads Capacitor 37 microfarad Capacitor 38 do Capacitor 40 do .05 Capacitor 48 do .05 Capacitor 49 do .05 Capacitor 50 do .05 Capacitor 51 do .05

Fig. 4 shows an alternative system of circuits for the second detector tube 20. The cathode 2 is maintained positive with respect to ground through the medium of potentiometer 3430. Grid 8 may be connected to a tap on coil 30 or to the top thereof and may be biased negatively with respect to the cathode by connecting its return circuit to a suitable source of negative potential in the power supply system through the medium of a filter comprising resistor 52 and by-pass capacitor 53. Grid 9 may be connected in parallel with grid 8, as shown, or may be used separately and given a fixed bias through any suitable system of connections, the choice being dependent upon the conditions of operation and the amount of amplification and output desired. Grid M, which may take the form of a screen as shown in Fig. 2, may be allowed to float at a potential intermediate to that of the anode 6 and cathode 2 by means of a resistor 54, connection as shown, or its potential may be substantially fixed with respect to the anode and cathode by using a potentiometer comprising resistors 54 and 51. Capacitors 3?, 55 and 56 serve to by-pass alternating currents in the cathode, screen grid and anode circuits. The auxiliary anode I2 may be coupled to any point on the system having A-C potential of suitable value for automatic volume control, as for example, to the top of coil 30 through the medium of capacitor 42, as shown.

. With the system of connection shown in Fig. 4, tube 20 functions as a plate type of detector to convert radio frequency potentials applied to the grids 8 and 9 into pulsating direct currents in load resistor 39. nents of the potentials across resistor 39 maybe coupled to a succeeding audio stage'by capacitor 49 and potentiometer 4|, as hereinbefore described in connection with'Fig. 3.

Whenever the peaks of the A-C potentials applied to auxiliary anode I2 exceed the amount by which the cathode 2 is maintained positive with respect to ground, electrons will be attracted to the auxiliary anode and a negative potential will then be applied to the automatic volume control circuits of the preceding tubes through the medium of resistor 44 and capacitor 48, all as here- 'inbeforedescribedin connection with Fig. 3.

Fig. 5 shows a system of connections whereby a tube of-the type shown in Fig. l, but with the auxiliary anode omitted, may be utilized for carrying out the purposes of the invention. In the arrangement shown in Fig. 5, coil 30 is opened at its electrical center and a by-pass capacitor 58 is inserted at this point. This capacitor serves to isolate the grids B and 9 from one another insofar as direct current potentials are concerned.

Through the medium of potentiometer 34-3536, the cathode '2is maintained at a positive potential with respect to ground. Grid r8, which is connected to ground through the signals are received, but electrons are attracted 40 V ceed the amount by whichicathode 2 is mainto grid 8 only when the peaks of'the signals extained positive with respect to ground. Grid 9, with cathode 2, thus serves as a half wave rectifier for all applied signals. Grid Sserves as a half wave rectifier forall applied signals whose peaks exceed its initial negative bias. Grid 8 may therefore be made to serve as a. source of negative potentials for an automatic volume con trol which functions only when the peaks of the sign-alslexceed a determinate value. In the system now being described, as well as in the previously described systems, the volume control potential may, if desired, be amplified by connecting the lower end of resistor 36 to a point in the power supply system which is negative with respect to ground as disclosed in my copending application S. No. 605,185 filed April 14, 1932..

It is customary in receivers employing commercial tubes of the typeswidely used at the time of filing this application 'to'provide means-of controlling the amount of amplification ahead of the detector. This is usually done by adjusting the potentials on the electrodes of the amplifier tubes by a potentiometer such as shown at 59, 69, 6| in Figures 3, 4, 5 and 6.

Many variations from the above will suggest themselves to those skilled in the art. For ex'-' ample, in Fig. 3, the grids 8 and 9 ofitube 29 may be given an initial negative bias-rather than a positive bias'as shown in the figure. Tube 20 will then act as a plate detector rather than as a grid detector. The tube 29 f Figsi3 and may include a screen, or the screen may be omitted from tube 20 of Fig. 4. Tube 20-ofFig. 5 may be made to function as a plate detector instead of a The audio-frequency compogrid detector by supplying negative potentials 7 means, and a detector-governor comprising dc tecting and governing sections substantially separate electronically and non-interacting; the detecting section comprising the cathode and detecting electrodes; the governing section'comprising a diode havingan anode closely surrounding the cathode and receiving'therefrom an electron stream separate from and non-interacting with electrons associated with the detecting section; a detector circuit comprising the cathode and detecting electrodes; a governor circuit comprising the cathode, the anode of the diode and means biasing said anode of the diode with respect to the cathode; and means coupling said anode of the-diode with the gain control means; whereby the controlling function is eifective only when selected peak potentials within the system fall within a'selected range, and whereby deleterious interactions are avoided- 2. In combination, an amplifier having gain control means, a detector having a cathode, detecting and amplifying electrodes and a negatively biased anode adjacent to the cathode but electronically separated from the other electrodes, 2. connection applying amplified signal potentials to the anode, and a connection from the anode to said gain control means in the amplifierwhereby the detector functions to control the gain of the amplifier whenever the peaks of potentials applied to the'detector exceed a determinate level.

3. A radio receiver including an automatic volume control comprising an amplifier having gain'control means, a detector having substantially electronically separate and non-interacting detecting and controlling means; the detecting means comprising a cathode and detectingelectrodes; the controlling means comprising said cathode and a cold electrode closely surrounding the cathode and having an electron stream substantially separate from and non-interacting with electrons associated with the detecting electrodes; adetector circuit comprising said cathode and detectingelectrodes and a controlling circuit comprising said cathode and cold electrode; means biasing the cold electrode relative to the cathode and a circuit including, the cold electrode and said amplifier gain control means.

4. Apparatus providing means to receive amplifying and detecting tubes and having contacts for the tube electrodes and circuits with means for detection and automatic'control of amplification,

' said means comprising an electron tube having a cathode, separate detecting and controlling electrodes including at least one cold electrode adjacent to the cathode, a source of potential for giving the'cold electrode aninitial negative bias with respect to the cathode, a connection from the output circuit contact for an amplifying tube to said cold electrode, and a connection from,

said cold electrode'to a gain control contact of an amplifying tube and a connection from an output circuit contact for an amplifying tube to a contact for a detecting electrode. 1

5. Amplifying and detectingapparatus adapted to utilize an electron tube having a cathode, at least one grid, and at least two anodes, at least one of which is adjacent to the cathode but electrically separated from the other electrodes, with means whereby the cathode, at least one anode and a grid serve for detection and amplification and means whereby amplification is automatically controlled whenever selected peak potentials within the apparatus exceed a chosen level, the last mentioned said means comprising a source of potential for biasing an anode adjacent to the cathode negatively with respect to the cathode, gain control means in the amplifying apparatus, an input circuit for said anode and cathode, and a connection from the anode to said gain control means of the amplifying apparatus.

6. Amplifying apparatus embodying an electron tube having a cathode with an extension, at least one grid and at least two anodes, at least one of which is adjacent to the extension of the cathode, with detecting and amplifying circuits utilizing at least one grid and anode, and means whereby one of the anodes adjacent the extension serves to control amplification automatically whenever selected potentials within the apparatus exceed a fixed peak value, said amplifying apparatus having an output circuit and a gain control means, and said automatic control means comprising a negative bias for one of said anodes adjacent the extension coupling means between one anode and said output circuit, and coupling means between one anode and said gain control means.

'7. Electronic amplifying apparatus comprising a tube having a cathode with an extended portion at least one grid and at least twio anodes, at least one anode being electrically associated with the cathode extension only, means for utilizing the cathode, at least one anode and at least one grid for detection, means for maintaining one of the anodes adjacent the extension negative with respect to the cathode, gain control means, means for applying amplified potentials to the last mentioned said anode, and means for applying rectified potentials from that anode to said gain control means.

8. A radio receiver with provisions for amplification and detection adapted to utilize an electron tube having a cathode with an extended portion, at least two anodes, at least one of which is electrically related to the cathode extension only, and at least one grid, with means for utilizing the cathode, at least one anode and a grid for detection, provisions for maintaining one of the anodes adjacent the extension negative with respect to the cathode, coupling means for applying amplified potentials to the last mentioned said anode and cathode, and means for applying rectified potentials therefrom to control amplification.

9. In combination, an amplifier having gain control means and a detector-governor-amplifier comprising a cathode having an extended portion, an anode, at least one control grid and at least one auxiliary anode electronically related to the cathode extension only, means for applying the output of the amplifier to an auxiliary anodie, detection means embodying the cathode at least one anode and grid, means for giving said auxiliary anode an initial negative bias with respect to said cathode, and a connection from said auxiliary anode to said gain control means whereby the gain of the amplifier is controlled automatically whenever potentials applied to the detector exceed a fixable level as determined by said bias.

10. In combination, an amplifier having gain control means and an output circuit, a detector including a cathode with an extended portion, an

anode, at least one auxiliary anode electronically related to the cathode extension but not to the other electrodes and a plurality of control grids, detecting circuits including the cathode and other electrodes coupled to the output circuit and means whereby an auxiliary anode serves to control the gain of the amplifier whenever peak potentials applied thereto exceed a predetermined level, said auxiliary anode control means comprising a coupling from the cathode and auxiliary anode to said output circuit of the amplifier, a source of negative biasing potential for the auxiliary anode, and means coupling the auxiliary anode to said amplifier gain control means.

11. Amplifying and detecting apparatus having gain control means and adapted to utilize a tube having a cathode, an anode, at least one rectifier electrode surrounding an extended part of the cathode and means for amplification with means whereby amplification is automatically controlled whenever potentials applied to one of the rectifier electrodes exceed a determinate peak value, said last mentioned means compising a coupling from said electrode to a pointof amplified potentials, means comprising a resistor traversed by cathode currents biasing said electrode negatively to the cathode, and means coupling said electrode to the said gain control means.

12. A detector-governor for amplifying and detecting apparatus comprising a tube having a cathode, a plurality of symmetrically arranged control grids, and two anodes, one of said anodes being adjacent to the cathode and having an input circuit and a gain control circuit, an output circuit for the other anode, an input circuit for the control grids, biasing means for the first said anode, an amplifier, a control circuit from the first said anode to said amplifier, and a volume control whereby the output of the apparatus may be adjusted manually.

l3. Amplifying and detecting apparatus comprising an amplifier having an output circuit and having amplification control means, an electron tube having a cathode, an anode and plurality of rectifier electrodes surrounding the cathode but electronically separated from other electrodes, means for amplifying rectified potentials and means whereby amplification is automatically reduced whenever potentials applied to the rectifier F electrodes exceed a determinate value, said last mentioned means comprising a coupling from the electrodes to said output circuit, means biasing at least one electrode negatively to the cathode, and means coupling said electrode with said first mentioned amplification control means.

14. In combination, an amplifier having an output circuit and a potentially operated gain control, an electron tube having a cathode, an anode, and two symmetrically arranged control grids coupled to said output circuit of the amplifier, circuits 1 embodying impedances and biasing means whereby one of the grids is negatively biased with respect to the cathode and the other grid is initially at cathode potential, and a connection from the first named grid to said potentially operated gain control means.

15. A radioreceivercomprising an electronic amplifier, an electron tube having a cathode, an anode, two rectifier electrodes surrounding the cathode but electrically isolated from other electrodes and amplifying means, with provisions whereby one of said electrodes serves as an automatic volume control whenever signals applied to the receiver exceed a determinate value, said provisions comprisingmeans biasingsaidelectrode negatively to the cathodethrough themedium of cathode currents, means coupling said electrode to the output of the amplifier and a connection including an impedance from said electrode to an input electrode in the amplifier.

1 6. In a radio receiver, a radio frequency amplifier with gain control means, an electron tube having a cathode and at least two anodes at least one of which is adjacent the cathode and establishes therewith an electron flow not appreciably afiected by other electrodes, audio frequency amplifying means, a source of direct current, a gain control circuit comprising a radio frequency coupling circuit from the amplifier to the cathode and an anode adjacent the cathode, a connection including an impedance and the source of direct current for biasing said anode, a connection including a impedance from said anode to the gain control means in the amplifier, a signal detecting and amplifying circuit comprising the cathode, a separate anode and the audio frequency amplifying means, and by-pass means effectively preventing interaction between the gain control circuit and the detecting and amplifying circuit.

17. A radio receiver comprising a radio frequency amplifier having gain control means, a detector-governor comprising an electron tube having a cathode and a plurality of rectifier electrodes, means coupling the cathode and rectifier electrodes with theoutput of the radio frequency amplifier, a detector-amplifier circuit comprising at least one rectifier electrode and audio amplifying means, a governor circuit including a source of biasing potentials, the cathode, a separate rectifier electrode and gain control means in the amplifier for automatically controlling amplification, and decoupling means effectively isolating electrical reactions in the detector-amplifier circuit from electrical reactions in the governor circuit.

18. In combination, an electronic amplifier having potentially operated gain control means, an electron tube having acathode, an anode and two grids symmetrically arranged, means coupling the grids to the amplifier, a tapped source of direct current, a connection including animpedance from the anode to a positive point in the source, a connection including an impedance from the cathode to a negative point in the source, a connection including an impedance from one grid to the cathode, a connection including an impedance from the second grid to a point more negative than the cathode, and a connection including animpedance from the circuit of the second grid to the gain control means in the amplifier.

19. In combination in an amplifier and detector system having automatic gain control, at least one amplifier tube having a cathode with a connection to a negative return bus, a detector-governor tube having a cathode with a connection including an impedance to said negative return bus, means maintaining said cathode positive relative to said bus, at least one diode electrode electronically associated with the cathode and electrically isolated from other electrodes, means of applying amplified potentials to said diode electrode, means of applying rectified potentials from said diode'electrode to the automatic gain control and means separate from the aforesaid diode electrode associated with the cathode for detecting amplified potentials.

20. In combination in a radio receiver, a power supply unit, a radio frequency amplifier with automatic gain control, a detector governor comprising a cathode, two rectifier electrodes adjacent the cathode but electrically isolated from other electrodes and detecting and amplifying means, means biasing the rectifier electrodes differentially with respect to one another and the cathode through the medium of energy drawn from the power supply unit, means utilizing at least one rectifier electrode for automatic gain control above a predetermined level and means utilizing at least one rectifier electrode for detection of signals.

HAROLD F. ELLIOTT. 

